U.S. patent application number 10/653564 was filed with the patent office on 2005-03-03 for polished downhole transducer having improved signal coupling.
Invention is credited to Fox, Joe, Hall, David R..
Application Number | 20050046590 10/653564 |
Document ID | / |
Family ID | 34217918 |
Filed Date | 2005-03-03 |
United States Patent
Application |
20050046590 |
Kind Code |
A1 |
Hall, David R. ; et
al. |
March 3, 2005 |
Polished downhole transducer having improved signal coupling
Abstract
Apparatus and methods to improve signal coupling in downhole
inductive transmission elements to reduce the dispersion of
magnetic energy at the tool joints and to provide consistent
impedance and contact between transmission elements located along
the drill string. A transmission element for transmitting
information between downhole tools is disclosed in one embodiment
of the invention as including an annular core constructed of a
magnetically conductive material. The annular core forms an open
channel around its circumference and is configured to form a closed
channel by mating with a corresponding annular core along an
annular mating surface. The mating surface is polished to provide
improved magnetic coupling with the corresponding annular core. An
annular conductor is disposed within the open channel.
Inventors: |
Hall, David R.; (Provo,
UT) ; Fox, Joe; (Provo, UT) |
Correspondence
Address: |
JEFFREY E. DALY
GRANT PRIDECO, L.P.
400 N. SAM HOUSTON PARKWAY EAST
SUITE 900
HOUSTON
TX
77060
US
|
Family ID: |
34217918 |
Appl. No.: |
10/653564 |
Filed: |
September 2, 2003 |
Current U.S.
Class: |
340/854.8 |
Current CPC
Class: |
E21B 17/028
20130101 |
Class at
Publication: |
340/854.8 |
International
Class: |
G08B 029/00 |
Claims
What is claimed is:
1. A transmission element for transmitting information between
downhole tools located on a drill string, the transmission element
comprising: an annular core constructed of a
magnetically-conductive material, the annular core forming an open
channel around the circumference thereof, the annular core further
configured to mate with a corresponding annular core along an
annular mating surface, thereby forming a closed channel; an
annular conductor disposed within the open channel; and the mating
surface being further polished to provide improved magnetic
coupling with the corresponding annular core.
2. The transmission element of claim 1, wherein the mating surface
is polished by at least one method selected from the group
consisting of grinding, lapping, hand polishing, annealing,
sintering, direct firing, wet etching, and dry etching.
3. The transmission element of claim 2, wherein the mating surface
is polished in multiple stages.
4. The transmission element of claim 2, wherein the mating surface
is treated to minimize alteration of magnetic properties of the
annular core.
5. The transmission element of claim 1, further comprising a
biasing member configured to urge the annular core toward a
corresponding annular core.
6. The transmission element of claim 5, wherein the biasing member
is selected from the group consisting of a spring, an elastomeric
material, an elastomeric-like material, a sponge, and a sponge-like
material.
7. The transmission element of claim 1, wherein the annular core
provides a low reluctance path for magnetic flux emanated from the
annular conductor.
8. The transmission element of claim 1, wherein the mating surface
is polished to reduce the dispersion of magnetic flux passing from
one mating surface to another.
9. The transmission element of claim 1, wherein the magnetically
conductive material is a ferrite.
10. The transmission element of claim 1, wherein the annular
conductor comprises multiple coiled conductive strands.
11. The transmission element of claim 1, wherein the open channel
has a substantially U-shaped cross-section.
12. A method for improving signal transmission between transmission
elements transmitting information between downhole tools, the
method comprising: providing an annular core constructed of a
magnetically conductive material, the annular core forming an open
channel around the circumference thereof, the annular core further
configured to mate with a corresponding annular core along an
annular mating surface, in order to form a closed channel;
providing an annular conductor in the open channel; and polishing
the mating surface to improve magnetic coupling with the
corresponding annular core.
13. The method of claim 12, wherein polishing further comprises at
least one technique selected from the group consisting of grinding,
lapping, hand polishing, annealing, sintering, direct firing, wet
etching, and dry etching.
14. The method of claim 13, wherein polishing further comprises
polishing the mating surface in multiple stages.
15. The method of claim 13, further comprising treating the mating
surface to minimize alteration of magnetic properties of the
annular core.
16. The method of claim 12, further comprising urging the annular
core toward a corresponding annular core.
17. The method of claim 16, wherein urging further comprises using
a biasing member to urge the annular core toward a corresponding
annular core, wherein the biasing member is selected from the group
consisting of a spring, an elastomeric material, an
elastomeric-like material, a sponge, and a sponge-like
material.
18. The method of claim 12, wherein the annular core provides a low
reluctance path for magnetic flux emanated from the annular
conductor.
19. The method of claim 12, wherein polishing reduces the
dispersion of magnetic flux passing from one mating surface to
another.
20. The method of claim 12, wherein the magnetically conductive
material is a ferrite.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] This invention relates to oil and gas drilling, and more
particularly to apparatus and methods for reliably transmitting
information between downhole drilling components.
[0003] 2. Background
[0004] Apparatus and methods are needed to effectively transmit
data along downhole-drilling strings in order to transmit data from
downhole components, such as tools located at or near a drilling
bottom hole assembly, to the earth's surface for analysis.
Nevertheless, the design of a reliable downhole transmission system
is difficult due to numerous design constraints. For example, drill
strings may include hundreds of sections of drill pipe and other
downhole tools connected together. Data must be transmitted
reliably across each tool joint to provide a continuous path
between downhole tools and the surface.
[0005] Reliably transmitting data across tool joints is difficult
for several reasons. First, since the tool joints are typically
screwed together, each of the tools may rotate with respect to one
another. In addition, as the tool joints are threaded together and
primary and secondary shoulders of the drilling tools come
together, the axial alignment of tools may be inconsistent.
Contacts or other types of transmission elements located at the
tool joint need to provide reliable connectivity despite the
relative rotation and inconsistent axial alignment of downhole
tools.
[0006] Moreover, the treatment and handling of drill string
components may be quite harsh. For example, as sections of drill
pipe or other tools are connected together before being sent
downhole, ends of the drill pipe may strike or contact other
objects. Thus, comparatively delicate transmission elements located
at the tool ends can be easily damaged. In addition, substances
such as drilling fluids, mud, sand, dirt, rocks, lubricants, or
other substances may be present at or between the tool joints. This
may degrade data connections at the tools joints. Moreover, the
transmission elements may be subjected to these conditions each
time downhole tools are connected and disconnected. Inconsistent
tolerances of downhole tools may also cause signal degradation as
signals travel up and down the drill string.
[0007] Inductive transmission elements provide one solution for
transmitting data between downhole tools. An inductive transmission
element functions by converting electrical signals to magnetic
fields for transmission across the tool joint. A corresponding
inductive transmission element located on the next downhole tool
converts the magnetic field back to an electrical signal where it
may be transmitted along the drill string.
[0008] In selected embodiments, an inductive transmission element
may include a conductor to carry an electrical current and a
magnetically conductive, electrically insulating material
surrounding the conductor to provide a magnetic path for the
magnetic field emanated from the conductor. The magnetically
conductive, electrically insulating material may reduce signal loss
associated with dispersion of the magnetic field.
[0009] In certain embodiments, an inductive transmission element
has an annular shape. The inductive transmission element is
inserted into an annular recess formed in the secondary shoulder of
the pin end or box end of a downhole tool. The annular shape allows
the inductive transmission element to always be oriented correctly
with respect to a corresponding inductive transmission element with
which it communicates. The placement of the inductive transmission
element on the secondary shoulder allows the element to be
protected within the downhole tool, and reduces stress that would
otherwise exist on the element if located on the primary
shoulder.
[0010] The use of inductive transmission elements at tool joints
may provide several advantages compared to the use of transmission
elements using direct electrical contacts. For example, inductive
transmission elements may provide more reliable contact than direct
electrical contacts. An inductive transmission element may not
require direct contact with another element, whereas the electrical
contact would always require direct contact. In addition,
electrical contacts may cause arcing that might ignite substances
present downhole such as flammable liquids or gases.
[0011] Since a drill string may extend into the earth 20,000 feet
or more, it is possible that a signal may pass through hundreds of
inductive transmission elements as the signal travels up or down
the drill string. The failure of a single inductive transmission
element may break the transmission path between the bottom hole
assembly and the surface. Thus, the inductive transmission element
must be robust, provide reliable connectivity, and provide
efficient signal coupling. Because signal loss may occur at each
tool joint, apparatus and methods are needed to reduce signal loss
as much as possible to reduce the need for frequent signal
repeaters along the drill string.
[0012] Thus, what are needed are apparatus and methods to improve
signal coupling in downhole inductive transmission elements.
[0013] What are further needed are apparatus and methods to reduce
the dispersion of magnetic energy at the tool joints.
[0014] What are further needed are apparatus and methods to provide
consistent impedance and contact between transmission elements
located along the drill string.
SUMMARY OF THE INVENTION
[0015] In view of the foregoing, it is a primary object of the
present invention to provide apparatus and methods to improve
signal coupling in downhole inductive couplers. It is a further
object of the invention to provide apparatus and methods to reduce
the dispersion of magnetic energy at the tool joints. It is yet
another object of the invention to improve current apparatus and
methods by providing consistent impedance and contact between
transmission elements located along the drill string
[0016] Consistent with the foregoing objects, and in accordance
with the invention as embodied and broadly described herein, a
transmission element for transmitting information between downhole
tools is disclosed in one embodiment of the invention as including
an annular core constructed of a magnetically-conductive material.
The annular core forms an open channel around its circumference and
is configured to form a closed channel by mating with a
corresponding annular core along an annular mating surface. The
mating surface is polished to provide improved magnetic coupling
with the corresponding annular core. An annular conductor is
disposed within the open channel.
[0017] In selected embodiments, grinding, lapping, hand polishing,
annealing, sintering, direct firing, wet etching, dry etching, or a
combination thereof, is used to polish the mating surface. In other
embodiments, the mating surface is polished in multiple stages. In
certain embodiments, the mating surface is treated to minimize the
alteration of magnetic properties of the annular core.
[0018] In selected embodiments, a transmission element in
accordance with the invention includes a biasing member configured
to urge the annular core toward a corresponding annular core. The
biasing member may be a spring, an elastomeric material, an
elastomeric-like material, a sponge, a sponge-like material, or a
combination thereof.
[0019] In certain embodiments, the annular core provides a low
reluctance path for magnetic flux emanated from the annular
conductor. The mating surface of the annular core may be polished
to reduce the dispersion of magnetic flux passing from one mating
surface to another. In selected embodiments, the magnetically
conductive material is a ferrite. In other embodiments, the annular
conductor comprises multiple coiled conductive strands. In yet
other embodiments, the open channel of the annular core has a
substantially U-shaped cross-section.
[0020] In another aspect of the invention, a method for improving
signal transmission between transmission elements includes
providing an annular core constructed of a magnetically conductive
material. The annular core forms an open channel around its
circumference and is configured to mate with a corresponding
annular core along an annular mating surface, in order to form a
closed channel. The method further includes polishing the mating
surface to improve magnetic coupling with the corresponding annular
core and placing an annular conductor in the open channel.
[0021] In selected embodiments, polishing may include a technique
such as grinding, lapping, hand polishing, annealing, sintering,
direct firing, wet etching, dry etching, or a combination thereof.
Polishing may also include polishing the mating surface in multiple
stages. In certain embodiments, a method in accordance with the
invention may include treating the mating surface to minimize the
alteration of magnetic properties of the annular core.
[0022] In selected embodiments, the method may include urging the
annular core toward a corresponding annular core. Urging may be
accomplished with a biasing member to urge the annular core toward
a corresponding annular core. The biasing member may be a spring,
an elastomeric material, an elastomeric-like material, a sponge, a
sponge-like material, or a combination thereof.
[0023] In selected embodiments, the annular core provides a low
reluctance path for magnetic flux emanated from the annular
conductor. In addition, polishing of the annular core may reduce
the dispersion of magnetic flux passing from one mating surface to
another. In certain embodiments, the magnetically conductive
material used to construct the annular core is a ferrite.
BRIEF DESCRIPTION OF THE DRAWINGS
[0024] The foregoing and other features of the present invention
will become more fully apparent from the following description,
taken in conjunction with the accompanying drawings. Understanding
that these drawings depict only typical embodiments in accordance
with the invention and are, therefore, not to be considered
limiting of its scope, the invention will be described with
additional specificity and detail through use of the accompanying
drawings in which:
[0025] FIG. 1 is a cross-sectional perspective view of one
embodiment of inductive transmission elements installed or
integrated into downhole tools;
[0026] FIG. 2 is a cross-sectional view illustrating the
relationship of inductive transmission elements communicating at
the tool joint;
[0027] FIG. 3 is a schematic perspective view illustrating the
theory of operation of inductive transmission elements in
accordance with the invention;
[0028] FIG. 4 is a schematic cross-sectional view illustrating the
magnetic field present around a conductive coil carrying a changing
electrical current;
[0029] FIG. 5 is a cross-sectional view illustrating one embodiment
of transmission elements in accordance with the invention forming a
closed magnetic path;
[0030] FIG. 6 is a cross-sectional view illustrating the transfer
of magnetic energy from one annular core to another when a gap is
present;
[0031] FIG. 7 is a cross-sectional view illustrating the transfer
of magnetic energy from one annular core to another when the mating
surfaces are irregular or rough;
[0032] FIG. 8 is a cross-sectional view illustrating the transfer
of magnetic energy from one annular core to another when the mating
surfaces are planar and conformal;
[0033] FIG. 9 is a cross-sectional view illustrating one embodiment
of the mating surface of an annular core;
[0034] FIG. 10 is a cross-sectional view illustrating one
embodiment of a rough untreated surface;
[0035] FIG. 11 is a cross-sectional view illustrating one
embodiment of a partially smoothed or treated surface;
[0036] FIG. 12 is a cross-sectional view illustrating one
embodiment of a fully smoothed or treated surface;
[0037] FIG. 13 is a cross-sectional view illustrating one
embodiment of a dead layer that may exist in a smoothed or treated
surface; and
[0038] FIG. 14 is a schematic block diagram illustrating various
surface smoothing and treating techniques.
DETAILED DESCRIPTION OF THE INVENTION
[0039] It will be readily understood that the components of the
present invention, as generally described and illustrated in the
Figures herein, could be arranged and designed in a wide variety of
different configurations. Thus, the following more detailed
description of embodiments of apparatus and methods of the present
invention, as represented in the Figures, is not intended to limit
the scope of the invention, as claimed, but is merely
representative of various selected embodiments of the
invention.
[0040] The illustrated embodiments of the invention will be best
understood by reference to the drawings, wherein like parts are
designated by like numerals throughout. Those of ordinary skill in
the art will, of course, appreciate that various modifications to
the apparatus and methods described herein may easily be made
without departing from the essential characteristics of the
invention, as described in connection with the Figures. Thus, the
following description of the Figures is intended only by way of
example, and simply illustrates certain selected embodiments
consistent with the invention as claimed herein.
[0041] Referring to FIG. 1, in order to connect sections of drill
pipe 10a, 10b and other downhole tools 10a, 10b together in series,
each typically includes a pin end 12 and a box end 14. The pin end
12 usually has external threads that thread into internal threads
of the box end 14. When connecting a pin end 12 to a corresponding
box end 14, various shoulders of the tools 10a, 10b meet to provide
additional structural support to the tools 10a, 10b.
[0042] For example, in selected downhole tools 10, the pin end 12
includes a primary shoulder 16 and a secondary shoulder 18.
Likewise, the box end 14 includes a corresponding primary and
secondary shoulder 20, 22. A primary shoulder 16, 20 is labeled as
such to indicate that it provides the majority of the additional
structural support to the drill pipe 10 or downhole component 10.
Nevertheless, the secondary shoulder 18 may also provide
significant support to the component 10.
[0043] In order to effectively monitor and control tools and
sensors that are located downhole, apparatus and methods are needed
to transmit information along the drill string. In order to achieve
this objective, reliable apparatus and methods are needed to
transmit information across tool joints where a pin end 12 connects
to a box end 14.
[0044] In selected embodiments in accordance with the invention, a
transmission element 24 is used to transmit data across a tool
joint. For example, the transmission element 24a may be installed
in the secondary shoulder of the pin end 12. This transmission
element 24a is configured to transmit data to a corresponding
transmission element 24b installed in the secondary shoulder 22 of
the box end 14. Cables 27a, 27b or other transmission media 27 are
connected to the transmission elements 24a, 24b to transmit data
along the tools 10a, 10b.
[0045] In certain embodiments, a recess is provided in the
secondary shoulder 18 of the pin end 12 and in the secondary
shoulder 22 of the box end 14 to accommodate each of the
transmission elements 24a, 24b. The transmission elements 24a, 24b
may be constructed in an annular shape to circumscribe the radius
of the drill pipe 10. Since the secondary shoulder 18 of the pin
end 12 may contact the secondary shoulder 22 of the box end 14, the
transmission element 24a may sit substantially flush with the
secondary shoulder 18 of the pin end 12. Likewise, the transmission
element 24b may sit substantially flush with the surface of the
secondary shoulder 22 of the box end 14.
[0046] In selected embodiments, the transmission element 24a
converts an electrical signal to a magnetic flux or magnetic field.
This magnetic field is detected by the corresponding transmission
element 24b. The magnetic field induces an electrical current in
the transmission element 24b. This electrical current is then
transmitted from the transmission element 24b to the electrical
cable 27b.
[0047] As was previously stated, downhole-drilling environments may
adversely affect communication between transmission elements 24a,
24b located on successive drill string components 10. For example,
materials such as dirt, mud, rocks, lubricants, or other fluids,
may inadvertently interfere with the contact or communication
between transmission elements 24a, 24b. In other embodiments, gaps
present between a secondary shoulder 18 on a pin end 12 and a
secondary shoulder 22 on a box end 14 may interfere with
communication between transmission elements 24a, 24b. Thus,
apparatus and methods are needed to reliably overcome these as well
as other obstacles.
[0048] Referring to FIG. 2, for example, as was previously stated,
a gap 28 may be present between the secondary shoulders 18, 22 of
the pin end 12 and box end 14. This gap 28 may be the result of
variations that are present in sections 10a, 10b of pipe. In other
embodiments, the gap 28 may be the result of materials such as
dirt, rocks, mud, lubricants, fluids, or the like, becoming
interposed between the shoulders 18, 22.
[0049] In some cases, the transmission elements 24a, 24b may be
designed such that optimal function occurs when the transmission
elements 24a, 24b are in direct contact with one another. Thus,
conditions that produce a gap 28 may cause malfunction of the
transmission elements 24a, 24b, thereby impeding or interfering
with the flow of data. Thus, apparatus and methods are needed to
improve the reliability of transmission elements 24a, 24b even in
the presence of gaps 28 or other interfering substances.
[0050] In certain embodiments, a transmission element 24a, 24b may
be moveable with respect to a shoulder 18, 22 into which it is
installed. Thus, the transmission elements 24a, 24b may be
translated such that they are in closer proximity to one another.
This may improve communication therebetween. In selected
embodiments, the transmission elements 24a, 24b may be designed
such that direct contact therebetween provides optimal
communication.
[0051] In other embodiments, some limited separation between
transmission elements 24a, 24b may still provide effective
communication. As illustrated, the transmission elements 24a, 24b
are mounted in the secondary shoulders 18, 22 of the pin end 12 and
box end 14, respectively. In other embodiments, the transmission
elements 24a, 24b may be installed in any suitable surface of the
pin end 12 and box end 14, such as in primary shoulders 16, 20.
[0052] Referring to FIG. 3, the function of the transmission
elements 24a, 24b may be illustrated by a first conductive loop
25a, and a second conductive loop 25b. The loops 25a, 25b may be
connected to a positive terminal 30a, 30b and a negative terminal
32a, 32b, respectively. When a voltage is applied across the
terminals 30a, 32a, a current is induced in the loop 25a. This
current may produce a magnetic field around the conductor forming
the loop 25a in accordance with the laws of electromagnetism. The
magnetic field produced by the loop 25a may induce an electrical
current in a second loop 25b, thereby creating a voltage across the
terminals 30b, 32b. Thus, an electrical signal transmitted along
the terminals 30a, 32a may be reproduced on the terminals 30b,
32b.
[0053] Although an electrical signal may be successfully
reproduced, the signal may lose a significant amount of power when
it is transmitted from one loop 25a to another 25b. One parameter
that may affect the amount of power that is lost is the distance 34
between the loops. In certain instances, closing the gap 34 may
significantly reduce loss.
[0054] Referring to FIG. 4, a cross-sectional view of the loops
25a, 25b is illustrated. As shown, a first current carrying loop
25b may produce a magnetic field around the conductor 25b as
illustrated by magnetic field lines 36a, 36b. A second loop 25a may
be positioned such that selected magnetic field lines 36a, 36b
enclose the loop 25a, while others do not. Those field lines 36
that enclose the loop 25a may be effective to induce a current in
the loop 25a, while those that do not enclose the conductor do not
induce a current and thus may be associated with signal loss. Thus,
in this example, the closer the loops are placed, the better the
signal coupling between the loops 25a, 25b.
[0055] Referring to FIG. 5, a cross-sectional view of one
embodiment of transmission elements 24a, 24b is illustrated. In
selected embodiments, transmission elements 24a, 24b in accordance
with the invention may include conductive loops 25a, 25b surrounded
by magnetically conductive cores 38a, 38b. The magnetically
conductive cores 38a, 38b may be inserted into housings 40a, 40b.
These housings 40a, 40b may sit within recesses 37a, 37b formed in
secondary shoulders 18, 22.
[0056] In selected embodiments, biasing members 42a, 42b may be
inserted between the housings 40a, 40b and the recesses 37a, 37b to
urge the transmission elements 24a, 24b together. In selected
embodiments, the housings 40a, 40b may be formed to include
shoulders 44a, 44b that may interlock with corresponding shoulders
46a, 46b, formed in the recesses 37a, 37b. This may prevent the
transmission elements 24a, 24b from exiting the recesses 37a, 37b
completely.
[0057] The magnetically conductive cores 38a, 38b may be used to
provide a magnetic path for the magnetic field emanating from the
conductors 25a, 25b. When a gap exists between the two cores 38a,
38b, the magnetic path is open and magnetic energy may be lost at
the gap. When the cores 38a, 38b come together, they formed a
closed path in which the magnetic flux 36 may travel. The better
the junction between the cores 38a, 38b, the lower the energy loss.
In certain embodiments in accordance with the invention, the
interface surfaces 48 between the cores 38a, 38b may be polished to
provide improved contact therebetween, and to reduce the loss of
magnetic energy.
[0058] The cores 38a, 38b may be constructed of any suitable
material having desired electrical and magnetic properties. For
example, in selected embodiments various "ferrites" may be suitable
for use in the present invention. These materials may provide
desired magnetic permeability, while being electrically insulating
to prevent shorting of electrical current carried by the conductors
25a, 25b.
[0059] Referring to FIG. 6, when a gap 50 is present between mating
surfaces of the cores 38a, 38b, significant magnetic energy may be
lost at the gap 50 as magnetic fringe patterns 36b attempt to span
the gap. As illustrated, selected magnetic field lines 36a may span
the gap 50, while others 36b may be dispersed, resulting in signal
loss. Thus, reducing the gap 50 as much as possible may improve
signal coupling between the cores 38a, 38b.
[0060] Referring to FIG. 7, in another embodiment, no gap is
present between the mating surfaces 52a, 52b of the cores 38a, 38b.
Nevertheless, surface imperfections, even microscopic
imperfections, may cause significant dispersion of magnetic energy
36b. This may also result in significant signal loss at the
junction 52a, 52b. Thus, mere contact between the surfaces 52a, 52b
may be insufficient.
[0061] Referring to FIG. 8, in another embodiment, the surfaces
52a, 52b may be polished or treated. In this embodiment, the
junction 52a, 52b may closely resemble a continuous core and
magnetic energy 36a may be efficiently coupled from one surface 52a
to the other. Thus, the combination of surface contact and having
surfaces 52a, 52b that are finely polished or treated may provide
the most efficient coupling of energy.
[0062] Referring to FIG. 9, in selected embodiments, a core 38 may
be produced that may appear to have a uniform or smooth surface.
However, upon magnification, the surface may exhibit significant
irregularities and imperfections that may result in significant
energy dispersion. Thus, a target surface 54 may be chosen and
material may be removed from the surface until the target surface
54, having a desired finish, is reached. In selected embodiments,
the core material 38 may be slightly oversize when manufactured,
thereby permitting a selected layer of material to be removed to
provide a desired finish.
[0063] Referring to FIG. 10, a surface may be treated or finished
in various stages to provide a desired finish. For example,
initially, the surface 52a may be characterized by a roughness
height 56a. Irregularities or peaks may be removed or smoothed
using some course method of smoothing or material removal. For
example, in selected embodiments, various methods of grinding may
be used to remove significant surface 52a imperfections or
irregularities. In selected embodiments, other techniques may be
used to remove material, such as direct firing, wet etching, dry
etching, or the like.
[0064] Referring to FIGS. 11 and 12, after a course method of
material removal has been completed, the surface 52b may be
characterized by a lesser roughness or irregularity height 56b. A
finer method of smoothing or material removal may be used to finish
this surface 52b. For example, the surface 52 may be lapped, hand
polished, finely sanded, or the like to remove these slight
irregularities. In addition, it is conceivable that a technique
such as annealing, sintering, direct firing, etching, or the like,
may be used to further smooth the surface to yield a desired finish
52c.
[0065] Referring to FIG. 13, smoothing the surface of the core 38
may provide various undesirable surface characteristics. For
example, surface techniques, such as grinding, may leave dead layer
58 in the magnetic material. The layer 58 may not be completely
"dead," but may have altered magnetic properties that may affect
proper signal coupling between the cores 38. The "dead layer" may
also exhibit undesired cracking or fractures. Thus, various
techniques may be used to reduce the dead layer 58 or prevent
occurrence of the dead layer 58. For example, in certain
embodiments, successively finer and softer abrasives may be used to
provide a desired surface finish and reduce the "dead layer" that
may otherwise occur.
[0066] Referring to FIG. 14, various surface treatment or smoothing
techniques may be used alone or in combination to provide a desired
finish to the core 38. For example, in selected embodiments,
techniques may include grinding, lapping, hand polishing,
annealing, sintering, direct firing, wet etching, dry etching, or
other techniques. Selected techniques may be used to remove
material, while others may be used to reduce or prevent a "dead
layer" in the magnetic material.
[0067] The present invention may be embodied in other specific
forms without departing from its essence or essential
characteristics. The described embodiments are to be considered in
all respects only as illustrative, and not restrictive. The scope
of the invention is, therefore, indicated by the appended claims,
rather than by the foregoing description. All changes within the
meaning and range of equivalency of the claims are to be embraced
within their scope.
* * * * *